Until now nobody can hack bitcoin wallet except due to errors and inability of wallet users, we never heard blockchain on hack, it proves that this system is very safe and can be used for safe and convenient transaction
Yes it's very safe and the only way hackers can hack wallets is due to negligence of the wallet owners, not the providers like blockchain.info. For example, I click something online and it turned out look like the main website of blockchain.info and I did input everything with my details there, hackers are just in standby and waits for their prey. That's how hackers can hack our bitcoin wallets.
If you link your blockchain.info wallet with gmail, it becomes extremely difficult for the hackers to steal your coins. If you can activate the Google Authenticator, then you can be 99.9999% sure that no one is going to hack your wallet.